inexpiable (adj.)

1560s, from Latin inexpiabilis "that cannot be atoned for," from in- "not" (see in- (1)) + expiabilis, from expiare "make amends for, purify, purge by sacrifice" (see expiation). The Inexpiable War was between Carthage and its Libyan mercenaries after the end of the First Punic War (241 B.C.E.). Related: Inexpiably.